Thehadith of thethaqalayn (Arabic:حديث الثقلين,lit. 'saying of the two treasures') refers to a statement, attributed to theIslamic prophetMuhammad, that introduces theQuran, the principal religious text inIslam, and his progeny as the only two sources of divine guidance after his death. Widely reported by bothShia andSunni authorities, the hadith of thethaqalayn is of particular significance inTwelver Shia, where theirTwelve Imams are viewed as the spiritual and political successors of Muhammad.
There exist several versions of this hadith inSunni sources.[1] The version that appears in theMusnad Ahmad ibn Hanbal, a canonical Sunni hadith collection, reads,
I [Muhammad] left among you two treasures which, if you cling to them, you shall not be led into error after me. One of them is greater than the other: The book of God (Quran), which is a rope stretched from Heaven to Earth, and [the second one is] my progeny, myAhl al-Bayt. These two shall not be parted until they return to the pool [of abundance in paradise,kawthar.[1]
Muhammad might have repeated this statement on multiple occasions,[1][2][3] including hisFarewell Pilgrimage and later at theGhadir Khumm, shortly before he died in 632.[2][4] The version of this hadith inAl-Sunan al-kubra, another Sunni hadith collection, adds the warning, "Be careful how you treat the two [treasures] after me."[5] Similar versions of the hadith can be found in other major Sunni sources, includingSahih Muslim,Sahih al-Tirmidhi, andSunan al-Darimi.[6] According to theTwelver Shi'a theologianMuhammad Husayn Tabataba'i (d. 1981), the hadith of thethaqalayn has been transmitted through more than a hundred channels by over thirty-fiveCompanions of the Prophet.[7]
Shia Islam limits the Ahl al-Bayt to theAhl al-Kisa, namely, Muhammad, his daughterFatima, her husbandAli, and their two sons,Hasan andHusayn.[8][9] In Shia theology works, the Ahl al-Bayt often also includes the remainingShia imams.[10] There are various interpretations in Sunni Islam, though a typical compromise is to include Muhammad's wives in the Ahl al-Bayt, in addition to the Ahl al-Kisa.[11] In some Sunni versions of the hadith, however,ahl al-bayt has been replaced withsunna; that is, practices of Muhammad.[11][12]
Some Sunni versions of the hadith of thethaqalayn replaceahl al-bayt withsunna, that is, practices of Muhammad.[11][12][13] This change is either intended to challenge the Shia implications of the hadith,[13] or, if authentic, may imply that theahl al-bayt of Muhammad are a source of hissunna.[14] Muhammad is indeed viewed as the 'living Quran', the embodiment of God's will in his behavior and words.[15] Both Sunni and Shia Muslims uphold the Quran and thesunna of Muhammad, though Shia extends thesunna to also include the traditions and practices of theirimams.[16]

InTwelver Shi'ism, the hadith of thethaqalayn establishes a parallel between the Quran and the family of Muhammad,[13] implying that the two serve as the only sources of divine guidance after Muhammad.[17] The hadith also implicitly describes (some) descendants of Muhammad as the true interpreters of the Quran,[18] and those descendants are viewed as the living embodiments of the Quran in Twelver Shi'ism.[13] As divine guides, those descendants must also be infallible lest they lead their followers astray.[17] The hadith also implies that Earth is never void of a descendant of Muhammad, an infallible imam, who serves as the divine guide of humankind in his time. These are theTwelve Imams in Twelver Shi'ism.[17] The last of these imams,Muhammad al-Mahdi, is believed to remain miraculously inoccultation since 874 and is expected to return in the end of times to eradicate injustice and evil.[19]
The belief in theMahdi remains popular among all Muslims, possibly owing to numerous traditions to this effect in canonical Sunni and Shia sources.[19]
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